The absorption spectrum of atomic sodium in the photon energy region from 30 to 150 eV has been investigated. A great number of sharp absorption lines which can be attributed to the excitation of a 2p-or a 2s-electron has been detected. Simultaneous excitation of one 2p-and one 3 s-electron gives rise to considerably strong broad and asymmetric absorption structures above the highest series limit (1P1) for the excitations of a single 2p-electron. Some of the assignments have been confirmed by Hartree-Fock calculations. The relative spectral dependence of the absorption cross-section in this energy range has been determined for the first time. The spectrum of free Na atoms has been compared with the LH, i~I spectrum of solid sodium.

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The absorption structure of five light metals has been measured from the onset of Kand LII, 111-absorption up to photon energies of 140 eV (170 eV for Be). The edges a t the threshold are followed by several broad peaks which are distributed over the total energy region covered by these measurements. There is a striking similarity between the LII,III-absorption spectra of Na, Mg, and Al; a similarity can also be seen between the K-absorption spectra of Li and Be.Das optische Absorptionsverhalten yon fiinf Leichtmetallen wurde vom Einsatz der Kbzw. LII,III-Absorption bis zu Photonenenergieii von 140 eV (bei Be bis 170 eV) gemessen. Neben den Kanten beim Einsatz wurden im ganzen Spektralbereich mehrere breite Absorptionsmaxima beobachtet. Der allgemeine Verlauf der L~~,~~~-Absorptionsspektren von Na, Mg und A1 stimmt gut iiberein; Ahnlichkeiten zeigen sich auch bei den K-Absorptionsspektren von Li und Be.

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